The present invention relates to a solder-containing heat-shrinkable tube used to connect electric wires or cables.
A solder-containing heat-shrinkable tube can solder and connect wires together and at the same time cover and protect the soldered portion with its tube adapted to shrink with soldering heat. It is therefore widely used for a permanent connection of electric wires. A ring-shaped solder piece is mounted in a heat-shrinkable tube as disclosed in e.g. Japanese Patent Publication No. 58-74245.
When connecting electric wires together with a solder-containing heat-shrinkable tube, wire ends are inserted into the tube while gripping the tube by a human or machine hand. Thus, the tube undergoes an external stress which tends to deform the solder piece in the tube. The deformed solder piece might chip off by contact with the wire ends. The solder piece in the conventional tube is prone to deformation because the solder and the tube contact each other along most of the entire inner circumference of the tube.
FIG. 6B shows one example of the prior art tube in which a solder ring 2 is in contact with a heat-shrinkable tube 1 over its entire inner circumference. FIG. 7 shows how the solder ring is deformed when subjected to an external force.
FIG. 8 shows another prior art tube in which the solder piece is inclined with respect to the tube with a smaller contact area on the inner wall of the tube. As shown in FIG. 9, it is liable to deformation under an external force, too.
The first object of the present invention is to provide a solder-containing heat-shrinkable tube in which the solder piece will not drop off due to deformation by external force.
The solder piece for use in a heat-shrinkable tube usually has a flux for good adhesion. The flux is either embedded in the solder piece or applied to its outer surface. In either case, the flux is exposed to the atmosphere in the conventional tube of this type.
FIGS. 10 and 11 show examples of such prior art tubes. In FIGS. 10A-10C, a heat-shrinkable tube 1 contains a ring-shaped solder piece 2 and a flux 3 embedded in the solder piece. The flux is exposed to the atmosphere even after the solder piece has been mounted.
In FIGS. 11A-11C, the heat-shrinkable tube 1 contains a solder piece 2 covered with a flux 3. The flux is in direct contact with the atmosphere at most of its outer periphery.
As the flux, an organic acid, amine, or amine halogenated hydracid family flux may be used. The flux of any type serves to remove any oxide layers on the wires to be connected and the solder piece. The function proceeds when it ionizes. The flux which is in a solid state at normal temperature ionizes rapidly when it melts with heat during use.
The flux ionizes gradually even while in storage by absorbing water in the air. The ionized component is consumed to remove only the oxide layer on the solder piece. Since the flux is thus consumed gradually while in storage, it cannot remove completely the oxide layers on the wires to be connected. This results in incomplete soldering. Thus, a conventional solder-containing heat-shrinkable tube has only a limited shelf life.
The simplest approach to this problem was to put a drying agent in its package. But such a method serves only to prolong its storage life up to about 10-40 per cent and is far away from a fundamental solution.
The second object of the present invention is to provide a solder-containing heat-shrinkable tube which can effectively protect the flux from deterioration and which has a longer storage life.